Illinois State Trooper Daniel Gillette stopped respondent for speeding on an interstate highway. When Gillette radioed the police dispatcher to report the stop, a second trooper, Craig Graham, a member of the Illinois State Police Drug Interdiction Team, overheard the transmission and immediately headed for the scene with his narcotics-detection dog. When they arrived, respondent’s car was on the shoulder of the road and respondent was in Gillette’s vehicle. While Gillette was in the process of writing a warning ticket, Graham walked his dog around respondent’s car. The dog alerted at the trunk. Based on that alert, the officers searched the trunk, found marijuana, and arrested respondent. The entire incident lasted less than 10 minutes.

Respondent was convicted of a narcotics offense and sentenced to 12 years’ imprisonment and a $256,136 fine. The trial judge denied his motion to suppress the seized evidence and to quash his arrest. He held that the officers had not unnecessarily prolonged the stop and that the dog alert was sufficiently reliable to provide probable cause to conduct the search. Although the Appellate Court affirmed, the Illinois Supreme Court reversed, concluding that because the canine sniff was performed without any “ ‘specific and articulable facts’ ” to suggest drug activity, the use of the dog “unjustifiably enlarg[ed] the scope of a routine traffic stop into a drug investigation.” 207 Ill. 2d 504, 510, 802 N. E. 2d 202, 205 (2003).

The question on which we granted certiorari, 541 U.S. 972 (2004), is narrow: “Whether the Fourth Amendment requires reasonable, articulable suspicion to justify using a drug-detection dog to sniff a vehicle during a legitimate traffic stop.” Pet. for Cert. i. Thus, we proceed on the assumption that the officer conducting the dog sniff had no information about respondent except that he had been stopped for speeding; accordingly, we have omitted any reference to facts about respondent that might have triggered a modicum of suspicion.

Here, the initial seizure of respondent when he was stopped on the highway was based on probable cause, and was concededly lawful. It is nevertheless clear that a seizure that is lawful at its inception can violate the Fourth Amendment if its manner of execution unreasonably infringes interests protected by the Constitution. United States v. Jacobsen, 466 U.S. 109, 124 (1984). A seizure that is justified solely by the interest in issuing a warning ticket to the driver can become unlawful if it is prolonged beyond the time reasonably required to complete that mission. In an earlier case involving a dog sniff that occurred during an unreasonably prolonged traffic stop, the Illinois Supreme Court held that use of the dog and the subsequent discovery of contraband were the product of an unconstitutional seizure. People v. Cox, 202 Ill. 2d 462, 782 N. E. 2d 275 (2002). We may assume that a similar result would be warranted in this case if the dog sniff had been conducted while respondent was being unlawfully detained.

In the state-court proceedings, however, the judges carefully reviewed the details of Officer Gillette’s conversations with respondent and the precise timing of his radio transmissions to the dispatcher to determine whether he had improperly extended the duration of the stop to enable the dog sniff to occur. We have not recounted those details because we accept the state court’s conclusion that the duration of the stop in this case was entirely justified by the traffic offense and the ordinary inquiries incident to such a stop.

Despite this conclusion, the Illinois Supreme Court held that the initially lawful traffic stop became an unlawful seizure solely as a result of the canine sniff that occurred outside respondent’s stopped car. That is, the court characterized the dog sniff as the cause rather than the consequence of a constitutional violation. In its view, the use of the dog converted the citizen-police encounter from a lawful traffic stop into a drug investigation, and because the shift in purpose was not supported by any reasonable suspicion that respondent possessed narcotics, it was unlawful. In our view, conducting a dog sniff would not change the character of a traffic stop that is lawful at its inception and otherwise executed in a reasonable manner, unless the dog sniff itself infringed respondent’s constitutionally protected interest in privacy. Our cases hold that it did not.

Official conduct that does not “compromise any legitimate interest in privacy” is not a search subject to the Fourth Amendment. Jacobsen, 466 U.S., at 123. We have held that any interest in possessing contraband cannot be deemed “legitimate,” and thus, governmental conduct that only reveals the possession of contraband “compromises no legitimate privacy interest.” Ibid. This is because the expectation “that certain facts will not come to the attention of the authorities” is not the same as an interest in “privacy that society is prepared to consider reasonable.” Id., at 122 (punctuation omitted). In United States v. Place, 462 U.S. 696 (1983), we treated a canine sniff by a well-trained narcotics-detection dog as "sui generis" because it "discloses only the presence or absence of narcotics, a contraband item." Id., at 707; see also Indianapolis v. Edmond, 531 U.S. 32, 40 (2000). Respondent likewise concedes that “drug sniffs are designed, and if properly conducted are generally likely, to reveal only the presence of contraband.” Brief for Respondent 17. Although respondent argues that the error rates, particularly the existence of false positives, call into question the premise that drug-detection dogs alert only to contraband, the record contains no evidence or findings that support his argument. Moreover, respondent does not suggest that an erroneous alert, in and of itself, reveals any legitimate private information, and, in this case, the trial judge found that the dog sniff was sufficiently reliable to establish probable cause to conduct a full-blown search of the trunk.

Accordingly, the use of a well-trained narcotics-detection dog–one that "does not expose noncontraband items that otherwise would remain hidden from public view," Place, 462 U.S., at 707–during a lawful traffic stop, generally does not implicate legitimate privacy interests. In this case, the dog sniff was performed on the exterior of respondent’s car while he was lawfully seized for a traffic violation. Any intrusion on respondent’s privacy expectations does not rise to the level of a constitutionally cognizable infringement.

This conclusion is entirely consistent with our recent decision that the use of a thermal-imaging device to detect the growth of marijuana in a home constituted an unlawful search. Kyllo v. United States, 533 U.S. 27 (2001). Critical to that decision was the fact that the device was capable of detecting lawful activity–in that case, intimate details in a home, such as “at what hour each night the lady of the house takes her daily sauna and bath.” Id., at 38. The legitimate expectation that information about perfectly lawful activity will remain private is categorically distinguishable from respondent’s hopes or expectations concerning the nondetection of contraband in the trunk of his car. A dog sniff conducted during a concededly lawful traffic stop that reveals no information other than the location of a substance that no individual has any right to possess does not violate the Fourth Amendment.

The judgment of the Illinois Supreme Court is vacated, and the case is remanded for further proceedings not inconsistent with this opinion.